block, proc and &

call method with block parameter:

two syntaxes:

1.  {   } 

     this is useful for one line

2. do   end

    this is useful for multiple line

ex:

["a", "b"].each do |i|

    puts "#{i}"

end

the element between |  | refers to each element in the array  

define a method with block parameter

use &

ex:

class Array

     def test( &arg)

           find_all( &arg)

     end    

end

pass proc parameter to a method received block

ex:

a=lambda{ puts "abc"}

test(&a)

lambda and proc

lambda:

parameter:  block

return: an instance of class Proc

Proc:

procedure

method:  

call:

tell proc to do sth

ex:

test = lambda { |i| i + 1 }

test.call(2)

--> 3

the method to pass parameters

1. test.call(2) 

2.  test[2]

another method to create Proc:

Proc.new {   }

IDE

textmate : 

mac, not free

aptana studio: 

 mac & windows, free

 include RadRails

3rdRail:  

mac & windows, free

NetBeans:

mac & windows, free

web api

open-uri

get date from URI

add   require 'open-uri'   in the program

YAML

load:

ex:

YAML.load(File.open("test.yaml") )

return the content in test.yaml

such as  "name:  peter" return  'name'=>'peter'

dump:

write to YAML file

ex:

File.open("test.yaml", w) {  |output|  YAML.dump(names, output) }

error handling: rescue & raise

handle exception:

ex:

begin

      puts  1/0

rescue

     puts "error"

end

--->  "error"

rescue can for specific exception:

ex:

begin

     puts 1/0

rescue  ZeroDivisionError

     puts "error"

end

rescue for method

ex:

def test

    puts "test"

rescue

    puts "rescue"

end

       

raise

raise exception

ex:

def test

   raise  ArgumentError,  "argument error"

end

the second argument is the message printed

get the exception

ex:

rescue ArgumentError =>  e

e is the exception 

define exception

ex:

class  TestException  <>

end

range

ex:

(‘A’..’Z’)

ex:

0..9